upd70f3422gj-gae-qs-ax Renesas Electronics Corporation., upd70f3422gj-gae-qs-ax Datasheet - Page 106

• Manufacturer Part Number: upd70f3422gj-gae-qs-ax
• Description: 32-bit Single-chip Microcontroller
• Manufacturer: Renesas Electronics Corporation.

Chapter 3
106
Table 3-2
Caution
3.2.1 General purpose registers (r0 to r31)
a)
b)
Each of the 32 general purpose registers can be used as a data variable or
address variable.
However, the registers r0, r1, r3 to r5, r30, and r31 may implicitly be used by
the assembler/compiler (see table Table 3-2). For details refer to the
documentation of your assembler/compiler.
General purpose registers
Before using registers r1, r3 to r5, r30, and r31, their contents must be saved
so that they are not lost. The contents must be restored to the registers after
the registers have been used.
Preliminary User’s Manual U17566EE1V2UM00
Register name
r0
r1
r2
r3
r4
r5
r6 to r29
r30
r31
Registers r0 and r30 are used by dedicated instructions.
Registers r1, r3, r4, r5, and r31 may be used by the assembler/compiler.
Usage
Zero register
Assembler-reserved register
User address/data variable register
Stack pointer
Global pointer
Text pointer
User address/data variable registers
Element pointer
Link pointer
Operation
Always holds 0. It is used for
operations using 0 and offset 0
addressing.
Used for 32-bit direct addressing.
Used to generate stack frame when
function is called.
Used to access global variable in
data area.
Used to indicate the start of the text
area (where program code is
located).
Base pointer when memory is
accessed by means of instructions
SLD (short format load) and SST
(short format store).
Used when calling a function.
b
CPU System Functions
b
a
b
a
b
b